1. Field of the Invention
The invention relates to a wheel having tension spokes, particularly such a wheel adapted to be used for a bicycle. More particularly, the invention relates to a wheel in which the rim and the spokes are made of a composite material.
2. Description of Background and Relevant Information
As is known in the art of bicycles in particular, the use of a composite material for the manufacture of bicycle components enables one to reduce the weight of such components, compared to such components being made of metallic materials. Further, a composite material, such as carbon fiber material, has a specific modulus and a specific strength that are higher than that of metals, such as that of aluminum which is typically used for wheel rims, or stainless steel that is typically used for spokes. Furthermore, composite materials have a better resistance to fatigue than metal.
It is thus known to make a bicycle wheel rim from a composite material. The following patent documents disclose rims of this type: FR 2 460 195; U.S. Pat. No. 4,314,964; FR 2 672 251; U.S. Pat. No. 5,249,846; FR 2 713 543; EP 1 231 077; and U.S. Pat. No. 6,761,847. To make the rim as a box-structure, sometimes a core on which the resin-coated composite layers are arranged is proposed; sometimes, an inflatable bladder that is arranged inside the mold and inflated is proposed.
Spokes made of a composite material are also known, as described in the patent documents WO 91/13771; U.S. Pat. No. 5,110,190; FR 2 784 622; and U.S. Pat. No. 6,036,281.
With respect to wheel assemblies made of a composite material, the patent document FR 2 701 899 discloses a compression-spoke wheel made by molding.
U.S. Pat. No. 5,104,199 discloses a wheel made in left and right halves that are joined together. Each half includes a rim portion and a set of spokes having a central portion for assembly to the hub. These elements are made all in one piece. During assembly, the two wheel halves are joined together, and the central portions of the spokes are mounted on a hub body, where they are kept spaced apart by means of two elastic blocking washers that are engaged in a groove. The spacing of the washers enables the spokes to be tensioned, which provides the wheel with rigidity.
In the same context, as shown in FIG. 24 U.S. Pat. No. 5,707,114 proposes to force the spacing of the central portions to enable the engagement of a tubular spacer in the center of the wheel.
U.S. Pat. No. 4,844,552 also discloses a wheel in which the tension of the spokes is adjusted by forcing the two spoke fastening flanges to be spaced apart in the area of the hub.
These methods of construction are advantageous as the resulting wheels are very light due to the absence of parts that enable the spoke tension to be adjusted. However, it is difficult to achieve a high spoke tension for a rear wheel in this fashion. Indeed, due to the presence of the free wheel, the central portion of the spoke set located on the side of the free wheel is close with respect to the median plane of the wheel, so that only a small amount of displacement is available for the portion to tension the spokes.
This problem is not specific to wheels made of a composite material. In general, the problem arises for any wheel whose spokes lack individual tension adjustability, at least on the side of the free wheel, and for which the spoke tension is adjusted by spacing apart the two spoke sets in the area of the hub.
In view of the prior art, there is a need for a wheel that makes it possible to achieve a higher spoke tension.